1. Field of the Invention
The present invention relates to a semiconductor device.
2. Description of the Related Art
A memory card (semiconductor memory card) having a NAND-type flash memory therein is downsized and provided with high capacity rapidly. For realization of a downsized memory card, semiconductor elements such as a memory element and a controller element are mounted in a stacked form on a wiring board. The electrode pads of the semiconductor elements are electrically connected to the connection pads of the wiring board by wire bonding. Besides, to provide the memory card with high capacity, the memory elements have come to be stacked into multiple layers on the wiring board.
The stacked number of memory elements is increasing and it is being studied to stack them into four, eight or more layers depending on the storage capacity of the memory card. To perform wire bonding of the semiconductor elements (memory elements) stacked into multiple layers, for example, a structure that the semiconductor elements are stacked into a step-like shape to expose the electrode pads of the semiconductor elements is applied (see JP-A 2001-217383(KOKAI), JP-A 2005-302871(KOKAI)). The semiconductor elements stacked on the wiring board are sealed with a mold resin after the electrode pads are electrically connected with the connection pads of the wiring board through metal wires.
The thickness of the semiconductor element such as a memory element tends to be decreased smaller and smaller in order to stack into multiple layers on the wiring board year by year. Besides, when plural semiconductor elements are stacked into a step-like shape, an end of the upper semiconductor element has an eaves-like state, namely a so-called overhang state, protruded from the lower semiconductor element. When the semiconductor elements whose thickness is decreased are stacked into a step-like shape, it is worried that various problems are caused due to the thickness and the overhang structure of the semiconductor elements. For example, there is a problem that the semiconductor element is warped or cracked at the time of wire bonding.
Besides, to realize a memory card with high capacity, provision of the memory element itself with higher integration and higher capacity based on it is being conducted in addition to the improvement of the stacked structure of the semiconductor elements on the wiring board. The outer shape of the memory element tends to become large when it is provided with high capacity. The outer shape of the memory card is specified, and its leading end is provided with a slope portion for indication of the forward and backward direction and the front and rear surface direction of the card (see JP-A 2007-293800(KOKAI)). In a case where a large memory element is mounted on a wiring board having a specified outside dimension, the slope portion which is provided at the leading end of the memory card becomes a factor of restricting the size of the semiconductor element mountable on the wiring board.